A formaldehyde-free Al³⁺/melamine aerogel with intrinsic flame retardancy and superior thermal insulation properties via a rapid ultrasound-assisted supramolecular self-assembly method

• Formaldehyde-free Al 3+ /MA aerogel was prepared by ultrasound-assisted self-assembly. • Unique needle-like architecture achieves exceptional compressive modulus. • Low-density AM aerogel (0.043 g/cm 3 ) achieves low thermal conductivity (0.033 W/m·K). • Excellent flame retardancy is confirmed by low PHRR (4.97 kW/m²) and high LOI (69.8%). With ultra-low density, high surface area, and tunable functionality, traditional melamine formaldehyde (MF) aerogels show excellent thermal insulation and fire resistance. However, their further applications are hindered by some issues, such as toxic formaldehyde usage, prolonged gelling time, and low mechanical strength. In this study, the gelling process was accelerated through ultrasound-assisted supramolecular self-assembly of aluminum nitrate and melamine (MA). A formaldehyde-free Al 3+ /MA (AM) aerogel was successfully fabricated using a straightforward freeze-drying method, which exhibited both intrinsic flame-retardant and superior thermal insulation properties. The low-density AM aerogel (0.043 g/cm 3 ) features a distinctive needle-like structure, which provides considerable compressive resistance and a high compressive modulus (33.63 kPa). In addition, it achieves a relatively low thermal conductivity (0.03343 W/m·K), an extremely low peak heat release rate (4.97 kW/m 2 ) and a high limiting oxygen index (69.8%), demonstrating its excellent flame-retardant performance. Moreover, the AM material demonstrates potential for a closed-loop lifecycle, allowing for its repeated regeneration after use. These results demonstrate that the AM aerogel is a high-performance flame-retardant material.